... , Low echo, clear speech, low price.*Built in digital audio disposal circuit , two step dynamic de ... voice.*Pinhole style, little volume, suitable for jail room and other small room.*Long ... twist line, etc.*Built-in over-loading protection and lightning proof circuit.*Pre-amplifier, directly drive DVR, ... ~75°C*According with FCC,CE standard. I.TRADIO pinhole,hidden,mini,built-in wall Audio Surveillance ...